Method of removing iron ions from a solution containing neodymium, praseodymium, dysprosium and iron

ABSTRACT

The present invention discloses a method of removing iron ions from a solution containing neodymium, praseodymium, dysprosium and iron, in which glucose is added into an acid solution containing neodymium, praseodymium, dysprosium and iron, at a molar ratio of iron/glucose at 0.2-2, and mixed evenly, and the solution is then hydrothermal treated, and after that an iron-containing precipitate is formed at the bottom, and the residual concentration of iron in the supernatant is less than 20 mg/L, and the retention rate of the rare earth elements is more than 97%. The present invention may separate iron from a solution containing neodymium, praseodymium, dysprosium and iron efficiently, which solves the pollution problem of iron to the extraction agent during the purification of the rare earth solution, and enhances the purity and utility value of the rare earth elements in the solution; the present invention is applicable to treat a rare earth solution containing a high concentration of iron or an acid solution of wastes, in which the retention rate of the rare earth elements is high, and the residual concentration of iron in the solution is low, with a simple operation and a low cost.

TECHNICAL FIELD

The present invention relates to the field of waste resourceutilization, particularly relates to method of removing iron ions from asolution containing neodymium, praseodymium, dysprosium and iron.

BACKGROUND

Iron is a metal commonly found in neodymium-containing rare earthwastes, which is high in content, similar to the rare earths in terms ofchemical valences, and difficult to be separated from the rare earths.It is the key to find a high-efficiency and stable iron separationmethod for recovering precious rare earth elements in rare earth wastesto obtain rare earth products in high-purity. Currently, in the reportediron separation methods from rare earth wastes, wet separation methodsinclude hydrochloric acid optimal solution method, sulfuric acid doublesalt precipitation, full extraction, phosphate precipitation, sulfideprecipitation and the like.

(1) The primary steps of hydrochloric acid optimal solution methodinclude oxidizing roasting (making the rare earth elements and iron tobe the highest valence) and separation for removing impurities(controlling the pH at 4-4.5, the rare earths in the roasting productsare dissolved preferentially). However, the pH controlling step iscomplex, and iron oxides may be dissolved during the dissolution of therare earths, such that the final solution may contain iron, which needto be further removed before extraction. Otherwise, the life of theextraction agent is inclined to be reduced during the extraction of therare earth solution containing iron.

(2) The primary steps of sulfuric acid double salt precipitation are:roasting (as above), dissolution (sulfuric acid dissolution, generatinga solution containing the rare earths and ferrous sulfate), double saltprecipitation (adding sodium sulfate into the solution, generating acomplex salt of sodium sulfate and neodymium sulfate). This method wouldgenerate ferrous sulfate when sulfuric acid is added for dissolution, Feelement would be wasted during the recovery of the rare earths, and itwould contaminate the environment after the discharge of ferrous sulfatesolution, making it hard to implement industrialization production.

(3) The primary steps of full extraction include: dissolving andleaching (adding hydrochloric acid to dissolve the wastes, and addinghydrogen peroxide to oxidize ferrous ions), extraction to remove iron(extracting iron into the organic phase with N₅₀₃ extraction agent) andextraction and separation of the rare earths (separating the single rareearth element with P₅₀₇ extraction agent). For iron-containing solutionwith high concentration, the consumption of the extraction agent N₅₀₃ ishigh, with high loss and cost.

(4) In the phosphate precipitation that has been reported, the rareearth waste containing iron is first dissolved, into which a reductiveagent is added to reduce ferric in the solution to ferrous, and thenphosphate is added to generate a rare earth phosphate precipitate. Therare earth phosphate precipitate produced by this method is not onlyinsoluble in acid, but also insoluble in alkali, thus it is difficult tobe processed to products with high added value.

(5) The primary steps of sulfide precipitation include adding acid todissolve the rare earth waste containing iron, then adding hydrogenperoxide or air aeration to oxidize ferrous, and then adding Na₂S togenerate a rare earth sulfide precipitate. There also would be ironsulfide precipitate generated in the rare earth precipitate, making thecontrolling conditions on obtaining the rare earths with high puritycomplex and difficult to implement.

(6) The primary steps of hydroxide precipitation include dissolving andleaching, ferrous oxidation and pH regulation. The key step is tooxidize the ferrous in the acid leaching solution and to control the pHof the solution within a range of 4-4.5 strictly, thus removing 98% ofiron in the supernatant. However, there is a drawback that there were aplenty of coordination sites on the surface of ferric hydroxideprecipitate, which may absorb the rare earth ions in water, causingabout 30%-50% of the rare earth ions co-precipitate with iron, thusdecreasing the recovery rate of the rare earths.

(7) With regard to oxalic acid precipitation, its basic steps are thesame as those in hydroxide precipitation, in which it also need tocontrol pH value strictly to generate a complex of oxalic acid—the rareearths. However, iron needs to be removed in advance when it is presentin a high concentration.

In the above various methods, when the rare earth wastes containing ironwere recycled, the first step is to dissolve the wastes with an acid,generating a solution containing iron and rare earth elements, and thento recycle the rare earths with an extraction agent. The processes ofseparating different rare earth elements using extraction techniqueswere sufficiently mature, while the extraction efficiencies tend to beinfluenced by iron ions in the solution, causing the extraction agent tobe poisoned after the combination of iron and the extraction agent, thusdecreasing the extraction efficiency of the rare earths. Against thehazard of iron in the extraction, some special iron extraction agentshave been developed, while they are expensive, and due to the highconcentration of iron in the solution, the application amount of theextraction agent is high, and the loss is also high.

Therefore, the prior art needs to be further improved and developed.

SUMMARY

In view of disadvantages of the above prior art, the present inventionaims to provide a method of removing iron ions from a solutioncontaining neodymium, praseodymium, dysprosium and iron, without theneed of controlling the pH range at the end of reactions, allowing ahigh retention rate of the rare earths, and decreasing the residualconcentration of iron in the solution.

To dissolve the above technical problems, the schemes of the presentinvention include:

Method of removing iron ions from a solution containing neodymium,praseodymium, dysprosium and iron, including the following steps:

A. taking a solution containing neodymium, praseodymium, dysprosium andiron, with a pH value between 0.1-3.5;

B. adding glucose to the solution from step A, and mixed evenly;

C. heating the mixed solution obtained from step B to 60° C.-350° C.,keeping the temperature constant for 5 minutes-72 hours;

D. after the solution from step C is cooled, a precipitate is formed atthe bottom, and the concentration of iron in the supernatant is lessthan 20 mg/L, the retention rate of the rare earth elements is more than97%.

The above described method, wherein, the solution from step A comprised,but not limited to, the solution generated after extraction of rareearth materials by an acid, wherein the acid refers to hydrochloric acidor nitric acid.

The above described method, wherein, the content of iron in the solutionfrom step A is between 0.15 g/L-300 g/L.

The above described method, wherein, the content of iron in the solutionfrom step A is between 4.2 g/L-300 g/L, in which ethylene glycol orascorbic acid is employed instead of glucose.

The above described method, wherein, the additive amount of ethyleneglycol is based on the molar ratio of iron/ethylene glycol at 0.5-3.8,after treatment with ethylene glycol, the residual concentration of ironin the supernatant is less than 500 mg/L.

The above described method, wherein, the additive amount of ascorbicacid is based on the molar ratio of iron/ascorbic acid at 0.1-1.5, aftertreatment with ascorbic acid, the residual concentration of iron in thesupernatant is less than 800 mg/L.

The above described method, wherein, after collected, the supernatant isaerated with air for 10 minutes-2 hours, and then adjusted to pH 4 withammonia water, generating an iron precipitate, while the rare earthsalso co-precipitating to generate a precipitate, the content of iron inthe supernatant is less than 15 mg/L, and the retention rate of rareearth elements is between 30%-52%.

The above described method, wherein, after the above precipitate isdissolved with hydrochloric acid or nitric acid according to thesolid-to-liquid ratio of 40%-70%, the concentration of iron in thesolution is more than 1500 mg/L, then it is treated according to step B,step C and step D, successively.

The above described method, wherein, the above step B particularlyfurther included: the additive amount of glucose is based on the molarratio of iron/glucose at 0.2-2, the glucose is mixed with wastescontaining neodymium, praseodymium, dysprosium and iron, into which thenan acid is added, and finally the glucose is heat treated according tostep C.

The above described method, wherein, the heating in the above step Cemploys a programmed heating, the heating conditions are confined asfollows: when the temperature is between 60° C.-120° C., the duration ofheating is not less than 10 hours; when the temperature is between 300°C.-350° C., the duration of heating may less than 30 minutes.

The present invention provides a method of removing iron ions from asolution containing neodymium, praseodymium, dysprosium and iron, inwhich glucose is added in the solution containing iron and rare earths,and the solution is heat treated to generate a precipitate, thusremoving iron from the solution efficiently. Compared with other methodsfor separating iron, the present invention may control the generation ofprecipitates without the need of regulating the pH, and there is nosignificant effect for the resulting precipitate on the concentration ofrare earth elements in the solution; the method of removing iron byadding ethylene glycol or ascorbic acid instead of glucose, proposed inthe present invention, may also remove iron from the rare earth solutionefficiently, while the residual concentration of iron in the supernatantis higher than that in the method in which glucose is added; and afterremoving iron by adding ethylene glycol or ascorbic acid, there remainsa portion of iron in the supernatant, which may be oxidized, and furtherthe pH may be adjusted with ammonia water, thus removing iron byconverting it into ferric hydroxide precipitate; the generatedprecipitate contains a large amount of iron and a few rare earthelements, after dissolution with an acid, a high concentration of ironin the dissolved solution could be removed by the method proposed in thepresent invention, to obtain a rare earth solution with a high purity;that is, iron could be separated from a solution containing neodymium,praseodymium, dysprosium and iron efficiently, which solves thepollution problem of iron to the extraction agent during thepurification of the rare earth solution, and enhances the purity andutility value of the rare earth elements in the solution, the retentionrate of the rare earths is high, and the residual concentration of ironin the solution is low, with a simple operation and a low cost.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is the concentration of iron in the solution after the additionof glucose, ethylene glycol and ascorbic acid according to the presentinvention;

FIG. 2 is the concentration of neodymium in the solution after theaddition of glucose, ethylene glycol and ascorbic acid according to thepresent invention;

FIG. 3 is the concentration of praseodymium in the solution after theaddition of glucose, ethylene glycol and ascorbic acid according to thepresent invention;

FIG. 4 is the concentration of dysprosium in the solution after theaddition of glucose, ethylene glycol and ascorbic acid according to thepresent invention;

FIG. 5 is the scanning electron microscope photograph of the precipitateproduced according to the present invention.

DETAILED DESCRIPTION

The present invention provides a method of removing iron ions from asolution containing neodymium, praseodymium, dysprosium and iron. Inorder to make the objectives, technical solutions and effects of thepresent invention clearer and definite, the present invention is furtherdescribed in detail below. It should be understood that the specificembodiments described herein are only used to explain the presentinvention and are not intended to limit the present invention.

The present invention provides a method of removing iron ions from asolution containing neodymium, praseodymium, dysprosium and iron,including the following steps:

A. taking a solution containing neodymium, praseodymium, dysprosium andiron, with a pH value between 0.1-3.5.

It is found during the experiment that when pH was less than 0.1, ironprecipitates could not occur after the hydrothermal reaction, and thusiron and the rare earths could not be separated.

When pH was greater than 3.5, ferric ions were precipitated in the formof ferric hydroxide in the hydrothermal reaction, thus causing twodrawbacks: (1) the rare earth elements in water were absorbed on thesurface of the new precipitated ferric hydroxide colloid; (2) the newgenerated ferric hydroxide colloid would enwrap the rare earth elementsin the solution during the condensation phase. Being affected by thesetwo drawbacks, the rare earth elements in the solution would return intothe ferric hydroxide precipitate, thus significantly decreasing theseparation efficiency.

Therefore, the pH of the solution containing neodymium, praseodymium,dysprosium and iron in the present invention is controlled between0.1-3.5.

B. glucose is added to the solution from step A, and mixed evenly;

Glucose is added to further promote the ferric ions in the solution toprecipitate, thus enhancing the separation efficiency of iron from thesolution. Specifically, glucose is used as the reductive agent to reduceferric iron on the surface of crystalline hematite to ferrous iron, inwhich ferrous iron may be bound with ferrous iron in the solution whenbeing oxidized with nitrate, forming a Fe—O—Fe bond, thus making thehematite crystals grow and decreasing the concentration of iron ions inthe solution.

C. the mixed solution obtained from step B is heated to 60° C.-350° C.,keeping the temperature constant for 5 minutes-72 hours;

When the temperature increased, the hematite crystal nucleus isgenerated from the ferric iron in the solution under the complexation ofnitrates, which crystallize and grow.

D. after the solution from step C is cooled, a precipitate is formed atthe bottom, and the concentration of iron in the supernatant is lessthan 20 mg/L, the retention rate of the rare earth elements is more than97%.

Further, the solution from step A comprised, but not limited to, thesolution generated after extracting the rare earth materials by an acid,wherein the acid refers to hydrochloric acid or nitric acid. And, thecontent of iron in the solution from step A is between 0.15 g/L-300 g/L.

Alternatively, the content of iron in the solution from step A isbetween 4.2 g/L-300 g/L, in which ethylene glycol or ascorbic acid isemployed instead of glucose. The additive amount of ethylene glycol isbased on the molar ratio of iron/ethylene glycol at 0.5-3.8, aftertreatment with ethylene glycol, the residual concentration of iron inthe supernatant is less than 500 mg/L. The additive amount of ascorbicacid is based on the molar ratio of iron/ascorbic acid at 0.1-1.5, aftertreatment with ascorbic acid, the residual concentration of iron in thesupernatant is less than 800 mg/L. After the supernatant is collected,it is aerated with air for 10 minutes-2 hours, and then adjusted to pH 4with ammonia water, making iron to precipitate, while the rare earthsalso co-precipitating to generate a precipitate, the content of iron inthe supernatant is less than 15 mg/L, and the retention rate of rareearth elements is between 30%-52%.

In particular, after the above precipitate is dissolved withhydrochloric acid or nitric acid according to the solid-to-liquid ratioof 40%-70%, the concentration of iron in the solution is more than 1500mg/L, then it is treated according to step B, step C and step D,successively.

Moreover, the above step B particularly further included: the additiveamount of glucose is based on the molar ratio of iron/glucose at 0.2-2,the glucose is mixed with a solution containing neodymium, praseodymium,dysprosium and iron, into which then an acid is added, and finally theglucose is heat treated according to step C. The heating in the abovestep C employs a programmed heating, the heating conditions are confinedas follows: when the temperature is between 60° C.-120° C., the durationof heating is not less than 10 hours; when the temperature is between300° C.-350° C., the duration of heating may less than 30 minutes.

In order to further describe the present invention, more detailedembodiments will be listed below for illustration.

Step 1. Dissolution of Neodymium-Iron Waste

5 kg of neodymium-iron waste was taken, and 50 L concentrated nitricacid was added at a weight-bulk ratio of 10%, and a solution containingneodymium, praseodymium, dysprosium and iron was obtained after thewaste was dissolved. Wherein, the pH value of the solution was 0.65, theconcentration of iron in the solution was 87760 mg/L, and theconcentrations of neodymium, praseodymium and dysprosium were 1882 mg/L,347 mg/L and 111.3 mg/L, respectively, as shown in FIGS. 1, 2, 3, and 4.

Step 2. Addition of Glucose

Based on the molar ratio of iron/glucose at 1, 15.6 kg glucose was addedwith stirring at 220 rpm for 1 hour.

Step 3. Heat Treatment

The solution of step 2 was transferred into a reactor, the fillingdegree of which was 50%, and which was heated in a closed state for 10hours at the heating temperature of 160° C. After completion of heating,the reactor was cooled to room temperature spontaneously. After thereactor was opened, it was found that the precipitate was separated wellfrom the solution and there was a light yellow precipitate forming atthe bottom. The morphology of the dry precipitate was shown in FIG. 5,being spherical particles with sizes of about 50 nm.

Step 4. Collection of the Supernatant

The top supernatant was pumped out of the reactor; the precipitate atthe bottom was mixed with water, filtered over a 0.45 μm filtermembrane, the filtrate was collected and mixed with the supernatant. ThepH of the mixture was 1.01, the concentration of iron in the mixture was17.2 mg/L (FIG. 1), and the concentrations of neodymium, praseodymiumand dysprosium were 1878 mg/L, 334 mg/L and 110.2 mg/L, respectively(FIG. 2, FIG. 3 and FIG. 4).

Step 5. Using Ethylene Glycol Instead of Glucose

Ethylene glycol was used instead of glucose, the additive amount ofwhich was based on the molar ratio of iron/ethylene glycol at 1.2, aftertreatment according to the methods of step 2 and step 3, the aqueoussolution was collected. The concentration of iron in the aqueous phasewas determined as 438 mg/L (FIG. 1), and the concentrations ofneodymium, praseodymium and dysprosium were 1851 mg/L, 337 mg/L and108.2 mg/L, respectively (FIG. 2, FIG. 3 and FIG. 4).

Step 6. Using Ascorbic Acid Instead of Glucose

Ascorbic acid was used to replace glucose, the additive amount of whichwas based on the molar ratio of iron/ascorbic acid at 1, after treatmentaccording to the methods of step 2 and step 3, the aqueous solution wascollected. The concentration of iron in the aqueous phase was detectedas 842 mg/L (FIG. 1), and the concentrations of neodymium, praseodymiumand dysprosium were 1812 mg/L, 326 mg/L and 106.9 mg/L, respectively(FIG. 2, FIG. 3 and FIG. 4).

Step 7. Cyclic Iron Removal and Purification of the Rare Earth Solution

The aqueous solution resulted from step 5 or step 6 was aerated with airfor 10 min at an aeration intensity of 1 L/min Ammonia water was thenadded to adjust the pH to 4, generating a precipitate of ferrichydroxide. The precipitate was collected, into which concentrated nitricacid was added at a volume ratio of precipitate/nitric acid at 0.5,stirred at a stirring rate of 220 rpm for 1 h, and the precipitate wasdissolved, the concentration of iron in the resulting solution was 7425mg/L, the concentrations of neodymium, praseodymium and dysprosium were215 mg/L, 56.6 mg/L and 25.5 mg/L, respectively. Then, ethylene glycolor ascorbic acid was used for treatment according to step 6 or step 7,the concentrations of iron in the supernatants were 414 mg/L and 895mg/L, respectively, and the concentrations of the rare earth elementssuch as neodymium, praseodymium and dysprosium remain unchangedbasically.

Of course, the above description was only the preferred embodiments ofthe present invention, which were not limited to the above embodiments.It should be noted that all the equivalent substitutions, obviousdeformation forms made by any person skilled in the art under theteachings of the present specification all fall within the essentialscope of the specification and should be protected by the presentinvention.

1. Method of removing iron ions from a solution containing neodymium,praseodymium, dysprosium and iron, which is characterized in that,including the following steps: A. taking a solution containingneodymium, praseodymium, dysprosium and iron, with a pH value between0.1-3.5; B. adding glucose to the solution from step A, and mixedevenly; C. heating the mixed solution obtained from step B to 60°C.-350° C., keeping the temperature constant for 5 minutes-72 hours; D.after the solution from step C is cooled, a precipitate is formed at thebottom, and the concentration of iron in the supernatant is less than 20mg/L, the retention rate of the rare earth elements is more than 97%. 2.The method according to claim 1, which is characterized in that, thesolution from step A comprised, but not limited to, the solutiongenerated after extracting the rare earth materials by an acid, whereinthe acid refers to hydrochloric acid or nitric acid.
 3. The methodaccording to claim 1, which is characterized in that, the content ofiron in the solution from step A is between 0.15 g/L-300 g/L.
 4. Themethod according to claim 1, which is characterized in that, the contentof iron in the solution from step A is between 4.2 g/L-300 g/L, in whichethylene glycol or ascorbic acid is employed instead of glucose.
 5. Themethod according to claim 4, which is characterized in that, theadditive amount of ethylene glycol is based on the molar ratio ofiron/ethylene glycol at 0.5-3.8, after treatment with ethylene glycol,the residual concentration of iron in the supernatant is less than 500mg/L.
 6. The method according to claim 4, which is characterized inthat, the additive amount of ascorbic acid is based on the molar ratioof iron/ascorbic acid at 0.1-1.5, after treatment with ascorbic acid,the residual concentration of iron in the supernatant is less than 800mg/L.
 7. The method according to claim 5, which is characterized inthat, after collected, the supernatant is aerated with air for 10minutes-2 hours, and then adjusted to pH 4 with ammonia water, makingiron to precipitate, while the rare earths also co-precipitating togenerate a precipitate, the content of iron in the supernatant is lessthan 15 mg/L, and the retention rate of rare earth elements is between30%-52%.
 8. The method according to claim 7, which is characterized inthat, after the above precipitate is dissolved with hydrochloric acid ornitric acid according to the solid-to-liquid ratio of 40%-70%, theconcentration of iron in the solution is more than 1500 mg/L, then it istreated according to step B, step C and step D, successively.
 9. Themethod according to claim 1, which is characterized in that, the abovestep B particularly further included: the additive amount of glucose isbased on the molar ratio of iron/glucose at 0.2-2, the glucose is mixedwith wastes containing neodymium, praseodymium, dysprosium and iron,into which then an acid is added, and finally the glucose is heattreated according to step C.
 10. The method according to claim 1, whichis characterized in that, the heating in the above step C employs aprogrammed heating, the heating conditions are confined as follows: whenthe temperature is between 60° C.-120° C., the duration of heating isnot less than 10 hours; when the temperature is between 300° C.-350° C.,the duration of heating may less than 30 minutes.